1. Field of the Invention
The present invention relates to a method of driving a switching device of a power supply apparatus and the power supply apparatus driven by the method.
2. Description of the Related Art
Conventionally, in the case where a plurality of converters are operated in parallel redundancy, each converter is connected to a load through a diode for reverse-current protection. However, the diode has so high a forward voltage drop that the power loss is large. As a measure against this, a semiconductor switching element such as MOSFET is used. In such a case, no problem would be posed if the MOSFET is turned on and connected in parallel to the converter added to the redundant system after the converter is fully activated and the voltage is established. In dynamic attachment and removal, however, the MOSFET is unavoidably turned on/off at a voltage lower than that of the redundant system considering the voltage detection error of the principal converter. A large charge current instantaneously flows through the capacitor of the activated converter from the redundant system, resulting in a large variation in load voltage.
Also in the case where the converter runs out of order when used with the MOSFET, the voltage across the converter gradually drops to such a level that the voltage across the faulty converter becomes lower than that across the redundant system, and the reverse current flows to the faulty converter through the MOSFET from the redundant system until the detection voltage for turning off the MOSFET is reached, thereby causing a large variation of the load voltage.
In the case where the faulty power supply is replaced for activation or the power supply runs out of order, the current of the redundant system is disturbed and the load voltage undergoes a variation when the MOSFET is turned on as described above. Thus, a noise is caused.
The object of the invention is to provide a highly reliable driving method for a semiconductor switching device used in a power supply apparatus at the time of preventing the reverse current and a power supply apparatus driven by the method.
According to one aspect of the invention, there is provided a driving method for the semiconductor switching device used in a power supply apparatus, in which the semiconductor switching device is not directly turned on but rather is turned on gradually through a non-saturated state.
More specifically, the semiconductor switching device, when turned on, is operated in a non-saturated area gradually in proportion to the difference between the output voltage or the output current of the power supply apparatus and a first reference value in the case where the output voltage or the output current is not less than a first reference value in the case where the output voltage or the output current of the power supply apparatus is not lower than the first reference value. Further, preferably, the semiconductor switching device is turned on fully in the saturated area in the case where the output voltage or the output current increases to not less than a second reference value.
According to another aspect of the invention, there is provided a driving method for the semiconductor switching device of a power supply apparatus, in which a first control signal corresponding to the difference between the output voltage or the output current of the power supply apparatus and the first reference value is applied to the semiconductor switching device at the time of activating the power supply apparatus. Further, a second control signal not smaller than the first control signal is applied to the semiconductor switching device at and after a time point when the output voltage or the output current reaches a second reference value larger than the first reference value.
In the driving method according to the invention, the current is limited when the semiconductor switching device starts to be turned on, and therefore it is possible to prevent such an abrupt current increase as to cause a load variation. The reliability of the power supply apparatus is improved by using the driving method according to the invention in the control circuit for controlling the on/off operation of the semiconductor switching device for outputting the power of the power supply apparatus.
Various semiconductor devices can be used as the semiconductor switching device including an insulated gate transistor such as a MOSFET (metal oxide semiconductor field effector transistor or IGBT (insulated gate bipolar transistor) and a bipolar transistor. In the power supply apparatus, the semiconductor switching device is used for various purposes including the reverse current blocking for parallel operation and various power control means. Also, the converter, the inverter, the switching power supply, and other various power converters and power control devices are used as the power supply apparatus.